Control system and method for controlling a screed head

ABSTRACT

A control system controls movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application. One of a pair of elevation receivers is mounted at each end of the screed head, providing a first and second signals indicating the position of the first and second ends of the screed head in relation to the reference. A sensor, mounted on the screed head, senses the orientation of the screed head along its length from the first end to the second end and providing a third signal indicating such orientation. A control circuit, responsive to the elevation receivers and to the sensor, controls the hydraulically moveable ends of the screed head using the first and second signals from the elevation receivers when the first and second signals are available, and controls the hydraulically movable ends of the screed head using the third signal from the sensor and one of the first and second signals from the elevation receivers when the other of the first and second signals is not available.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a control system for controlling movement of a tool carried by a machine and, more specifically, to a control system for controlling movement of individual hydraulically moveable ends of a tool which carries laser receivers, even when one of the receivers does not receive the transmitted plane of reference light.

[0002] In concrete paving operations, after concrete is poured, it is commonly finished by drawing a tool, such as a screed head, over the surface of the concrete. This smooths the surface of the concrete before it cures. In asphalt paving operations, after asphalt is laid, it is commonly leveled to a desired depth by drawing a tool, such as also a screed head of a paver, over the surface of the contour. Finally, in grading operations, a surface is graded to a desired depth by drawing a tool, such as a blade of a grader, over the surface of the contour. Thus, although the physical configurations of the types of screed heads and the grader's blade are not identical, the functions of these tools are analogous.

[0003] Typically, hydraulic cylinders connected to each end of the tool of the machine are used to raise and lower the ends of the tool independently. It has been common to determine the elevational positions of the ends of the tool by using a laser transmitter which provides a rotating beam of laser light, effectively producing a reference plane. The raising and lowering of the tool are controlled by a control system that has a predetermined desired elevational position for the surface.

[0004] A pair of laser receivers, one receiver mounted at each end of the tool on an associated mast for vertical movement with the tool, detects the reference plane and the relative elevation of the ends of the tool with respect to the reference plane. A control system of the machine then actuates hydraulic valves to supply fluid to the hydraulic cylinders in response to these detected levels. As a result, the elevation of each end of the tool can be precisely controlled. Each of the receivers provides elevational feedback to drive the hydraulics controlling the elevation of the end of the tool with which it is associated.

[0005] A problem arises, however, if one the receivers is blocked by something of an appreciable height, such as, for example, a support column in a building. When a blockage occurs, there is a need to maintain the relative elevation of the ends of the tool as it is drawn toward the machine until the laser beam can be reacquired by both receivers mounted at the ends of the tool.

[0006] One approach to this problem is to set up two laser transmitters at the same elevation on opposite sides of the tool. In this way, if a column blocks one of the transmitters, the other transmitter is likely to be illuminating the receivers at the ends of the tool, thereby compensating for the blockage. Essentially, this eliminates all blind spots around the receivers. While generally effective, this prior art method is disadvantageous in that by requiring an additional transmitter, the cost of the equipment is increased. Further, this method increases significantly the time required to set up the equipment and eliminate the possibility of a column block with the second laser transmitter.

[0007] It is seen, therefore, that there is a need for a control system and method for controlling movement of individually hydraulically moveable ends of a tool, such as a screed head, to maintain a selected elevational position between each end of the tool and an elevation reference even when one of the elevation receivers mounted on the ends of the tool fails to sense the position of the end of the tool.

SUMMARY OF THE INVENTION

[0008] This need is met by a control system according to the present invention for controlling movement of individual hydraulically moveable ends of a tool, such as a screed head. The screed head is carried by a boom of a machine in a concrete paving application to maintain a selected elevational position between each end of the screed head and a reference as the screed head is moved toward the machine. The control system includes an elevation receiver, mounted on a first end of the screed head, providing a first signal indicating the position of the first end of the screed head in relation to the reference, and an elevation receiver mounted on a second end of the screed head, providing a second signal indicating the position of the second end of the screed head in relation to the reference. A sensor is mounted on the screed head. The sensor senses the orientation of the screed head along its length from the first end to the second end and provides a third signal indicating this orientation. A control circuit is responsive to the elevation receivers and to the sensor and controls the hydraulically moveable ends of the screed head using the signals. The control circuit uses the first and second signals from the elevation receivers when the first and second signals are available. The control circuit uses the third signal from the sensor and one of the first and second signals from the elevation receivers when the other of the first and second signals is not available.

[0009] The control circuit preferably maintains the screed head in an orientation such that the third signal remains substantially constant when one of the first and second signals from the elevation receivers is not available. In this manner, the orientation of the screed head along its length from the first end to the second end is maintained substantially constant.

[0010] The sensor may be an inclinometer mounted on the screed head. Preferably, the inclinometer is a pendulum sensor with a low pass filtered output.

[0011] Preferably, the receivers are light detectors, and the reference is established by a beam of light. Even more preferably, the receivers are laser light detectors and the reference is established by a beam of laser light.

[0012] A method of controlling the elevational position of hydraulically moveable ends of a tool according to the present invention in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, includes the steps of: (a) selecting a desired elevational position of the tool with respect to the reference; (b) sensing with the elevation receivers the position of the ends of the tool in relation to the reference; (c) sensing the orientation of the tool along its length from one end to the other; and (d) controlling the elevational positions of the ends of the tool using the sensed positions of the ends of the tool in relation to the reference when such positions are both known, and controlling the elevational positions of the ends of the tool using the sensed position of one of the ends of the tool and the sensed orientation of the tool along its length from one end to the other when such positions are not both known. The method may further include the steps of (e) detecting lateral movement of the tool generally in the direction of the length of the tool; and (f) discontinuing controlling the elevational positions of the ends of the tool using the sensed orientation of the tool until the lateral movement of the tool generally in the direction of the length of the tool is terminated.

[0013] The step of sensing the orientation of the tool along its length may include the step of sensing the orientation of the tool using an inclinometer. The elevation receivers preferably are light detectors and the reference is preferably a rotating beam of light. Even more preferably, the elevation receivers may be laser light detectors and the reference may be a rotating beam of laser light.

[0014] Other objects, features and advantages will appear more fully in the course of the following discussion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 illustrates a screeding operation of a typical concrete screed utilizing the control system of the present invention;

[0016]FIG. 2 is an enlarged partial view of an inclinometer mounted on the screed head;

[0017]FIG. 3 is a schematic representation of an inclinometer and associated circuitry of the type incorporated in the present invention;

[0018]FIG. 4 is a schematic representation of a screed head, and elevation receivers, illustrating a technique for adjusting for offsets in inclinometer mounting; and

[0019]FIG. 5 is a flow chart diagram illustrating operation of the system of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0020] Referring to FIG. 1 of the drawings, the device implementing the preferred embodiment of invention herein is a control system for a machine 2, such as a concrete screed 4, that typically incorporates a laser transmitter 10 mounted in a stationary position. The transmitter 10 projects a rotating laser beam 12, in order to provide a reference. A pair of elevation receivers, such as laser receivers 14 and 15, and a control box 16 including a control circuit are provided for controlling electro-hydraulic control values (not shown) of the concrete screed 4. The concrete screed 4 further includes a pair of masts 18, each carrying one of the pair of laser receivers 14 and 15, attached with and moved generally vertically, independently, with respective ends 20 and 21, respectively, of a tool or screed head 22. The screed head 22 is attached to the end of a hydraulic boom arm 23 which moves the screed head 22 in longitudinal direction Y. During operation of the screed, the control box 16 causes actuation of the hydraulic valves such that hydraulic cylinders 24 and 25 at the ends 20 and 21, respectively, independently raise or lower the ends 20 and 21 of the screed head 22, as needed, as it is drawn in the direction Y over the surface of uncured concrete 26. It is to be appreciated that the raising and lowering of the screed head 22 in the vertical direction are accomplished in response to reception of the reference laser beam 12 by the pair of laser receivers 14 and 15. The laser beam 12 rotates about an axis, as indicated at 28, so as to define the reference as a reference plane of laser light. The first and second receivers 14 provide respective first and second signals indicating the position of the respective ends of the screed head 22 in relation to the reference 12.

[0021] As discussed above, a difficulty arises with the conventional control system of this type when the path of the laser beam 12 to one of the pair of elevation receivers 14 is temporarily blocked by a column or other obstruction at a work site. In the present invention, this difficulty is addressed by the use of a sensor 30, mounted on the screed head 22, for sensing the orientation of the screed head 22 along its length from the first end to the second end. The sensor 30 preferably is an inclinometer that is mounted on the screed head as best shown in FIG. 2. The sensor 30 provides a third signal that indicates the orientation of the screed head. A control circuit in box 16 is responsive to the elevation receivers 14 and 15 and to the sensor 30 for controlling the hydraulically moveable ends 20 and 21 of the screed head 22 using the first and second signals from the elevation receivers 14 and 15 when the first and second signals are available, and for controlling the hydraulically movable ends 20 and 21 of the screed head 22 using the third signal from the sensor 30 and one of the first and second signals from the elevation receivers 14 and 15 when the other of the first and second signals is not available. The control circuit maintains the screed head 22 in an orientation such that the third signal remains substantially constant when one of the first and second signals from the elevation receivers 14 and 15 is not available. By this approach, the screed head is also maintained in a substantially constant orientation along its length from the first end to the second end.

[0022] As stated above, the sensor 30 is preferably an inclinometer. An appropriate inclinometer 32 and associated circuitry is shown in FIG. 3. As will be apparent, the inclinometer 32 is a pendulum sensor that incorporates a pendulum arm 34 which pivots about axis 36, moving rotor 38. Rotor 38 includes a plurality of windings 40 which rotate with the rotor and cooperate with a permanent magnet stator 42. The output of the windings 40 is supplied to with a low pass filter 44 and is then digitized in A-D converter 46. As will be appreciated phototransistors 48 cooperate with LED's 50 to determine when the inclinometer has been pivoted sufficiently that the pendulum 34 does not prevent the light from the LED's 50 from striking the transistors 48. When one of the transistors 48 is illuminated, a signal is applied to amplifier 52 which then drives windings 40 until the pendulum 34 is brought back into position to shield both of the phototransistors 48. The amplitude of this driving current provides an indication of the degree of inclination of the sensor 30.

[0023] It will be appreciated that the sensor 30 may not be mounted in perfectly horizontal position on the screed head 22. If one were to assume that when the receivers 14 and 15 were on grade, i.e., at a position that indicates by appropriate receipt of the laser beam 12 that the screed head 22 is positioned at the correct height and orientation, the inclinometer 30 would read zero slope, and the algorithm of the slope control system would be relatively simple. The controller would simply drive until the slope sensor read zero whenever one of the laser receiver signals was lost. This assumption is not always correct. Rather, the laser plane will have some finite slope to it resulting in elevation offsets and the slope sensor that is mounted to the screed head will also have some slope offset to it (due to the mechanical mounting characteristics). The following algorithm has been provided to deal with these issues.

[0024] Variable Definitions:

[0025] All angles in the remainder of this document are expressed in terms of slope (rise over run) and are referenced to horizontally flat.

[0026] Δ_(LrLeft) is the deviation from On-Grade point of the laser receiver on the left side.

[0027] Δ_(LrRight) is the deviation from On-Grade point of the laser receiver on the right side.

[0028] Δ_(Lr) is the total vertical error as measured by the laser receivers. It is equivalent to Δ_(LrRight)-Δ_(LrLeft).

[0029] w is the width of the controlled item.

[0030] θ_(measured) is the angle that is measured by the slope sensor mounted to the controlled item.

[0031] θ_(sensor) _(—) _(offset) is the angular offset of the slop sensor. It is equal to θ_(measured) when the controlled item is perfectly flat.

[0032] w′ is the length of the base of a right triangle created from a hypotenuse w and the angle (θ_(measured)-θ_(sensor) _(—) _(offset)). This is in essence the horizontal component of the controlled item when the controlled item is elevated on one end.

[0033] θ_(grade) is the angle generated from the slope laser beam plane.

[0034] θ_(measured)-θ_(sensor) _(—) _(offset) is equivalent to θ_(grade) when the implement is on-grade.

[0035] If Δ_(Lr) is small compared to w, then the approximation w≈w′ can be made.

[0036] When the laser strikes both laser receivers 14 and 15 at approximately the same time, the data θ_(measured), Δ_(Lr), and w are available.

[0037] With this data, θ_(offset) can be calculated as follows:

[0038] θ_(sensor) _(—) _(offset)=θ_(measured)−θ_(grade)

[0039] but θ_(grade) is equivalent to $\frac{\Delta_{LR}}{w}.$

[0040] This makes the assumption that the distance from On-Grade point of the receivers to the cutting edge of the screed head is equivalent on both sides. If this is not the case, an additional offset is created which can be combined with θ_(sensor) _(—) _(offset) to produce a single angular offset.

[0041] Therefore by substituting the following can be derived, $\theta_{sensor\_ offset} = {\theta_{measured} - \frac{\Delta_{LR}}{w}}$

[0042] Now that θ_(sensor) _(—) _(offset) is known, if on the next laser sweep, one of the laser signals is missing, the system can drive screed head 22 using a calculated Δ_(LR) as Δ_(LR)=θ_(measured)−θ_(sensor) _(—) _(offset).

[0043] Reference is now made to FIG. 5, which is a flow chart diagram illustrating the manner in which the operator smooths the concrete surface as he repeatedly pulls the screed head 22 toward the machine 4. The operator extends the boom 23 and toggles the land switch on control box 16, as indicated at 54. A timer and a lower valve drive are initiated. If either receiver 14 or 15 has detected the laser reference 12 at 56, but not both, then the data from the sensor 30 is used at 58 and 60 in place of the missing data from the receivers. The valve drives for both sides of the screed head are stopped at 62 when the screed head is one inch from being at the correct height, i.e., “on grade.” The system is then placed in automatic mode, and the screed head is slowly lowered to the on-grade height. The hydraulic boom arm 23 is then retracted and the screed head smooths the concrete surface 26. If a signal from one of the receivers 14 and 15 is not available during this operation the control circuit maintains the screed head in an orientation such that the third signal from the sensor 30 remains constant. By this approach, the slope of the screed head along its length from the first end to the second end also is maintained substantially constant until the receiver 14 or 15 reacquires the beam 12.

[0044] Depending upon the configuration of the structure around the concrete surface being smoothed by the screed head, it may not be possible to move the screed head in a straight line toward the machine. It may, for example, be necessary for the operator to shift the beam 23 from side to side to avoid columns and the like as the screed is moved. This will, of course, induce an error in the output of the sensor 30. To avoid this, the lateral movement of the screed head generally in the direction of the length of the screed head 22 is detected. Controlling the elevational positions of the ends of the screed head using the sensed orientation of the screed head is discontinuing until this lateral movement is terminated. With many screed machines the operator must actuate a switch to activate the hydraulic valves to rotate the screed head. The control circuit senses actuation of this switch, and discontinues use of the output of the sensor 30 until rotation of the screed head 22 is terminated.

[0045] Having described the invention in detail and by reference to preferred embodiments thereof, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. 

What is claimed is:
 1. A control system for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, comprising: an elevation receiver, mounted on a first end of the screed head, providing a first signal indicating the position of the first end of the screed head in relation to the reference; an elevation receiver, mounted on a second end of the screed head, providing a second signal indicating the position of the second end of the screed head in relation to the reference; a sensor, mounted on the screed head, for sensing the orientation of the screed head along its length from the first end to the second end and providing a third signal indicating such orientation; and a control circuit, responsive to the elevation receivers and to the sensor, for controlling the hydraulically moveable ends of the screed head using the first and second signals from the elevation receivers when the first and second signals are available, and for controlling the hydraulically movable ends of the screed head using the third signal from the sensor and one of the first and second signals from the elevation receivers when the other of the first and second signals is not available.
 2. The control system according to claim 1 for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, in which the control circuit maintains the screed head in an orientation such that the third signal remains substantially constant when one of the first and second signals from the elevation receivers is not available, whereby the orientation of the screed head along its length from the first end to the second end also is maintained substantially constant.
 3. The control system according to claim 1 for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, in which the sensor is an inclinometer mounted on the screed head.
 4. The control system according to claim 3 for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, in which the inclinometer is a pendulum sensor with a low pass filtered output.
 5. The control system according to claim 1 for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, in which the receivers are light detectors, and in which the reference is established by a beam of light.
 6. The control system according to claim 1 for controlling movement of individual hydraulically moveable ends of a screed head carried by a boom of a machine so as to maintain a selected elevational position between each end of the screed head and a reference in a concrete paving application as the screed head is moved toward the machine, in which the receivers are laser light detectors and in which the reference is established by a beam of laser light.
 7. A control system for controlling movement of individual hydraulically moveable ends of an elongated tool so as to maintain a selected elevational position between each end of the tool and a reference, comprising: an elevation receiver, mounted on a first end of the tool, providing a first signal indicating the position of the first end of the tool in relation to the reference; an elevation receiver, mounted on a second end of the tool, providing a second signal indicating the position of the second end of the tool in relation to the reference; a sensor, mounted on the tool, for sensing the orientation of the tool along its length from the first end to the second end and providing a third signal indicating such orientation; and a control circuit, responsive to the elevation receivers and to the sensor, for controlling the hydraulically moveable ends of the tool using the first and second signals from the elevation receivers when the first and second signals are available, and for controlling the hydraulically movable ends of the tool using the third signal from the sensor and one of the first and second signals from the elevation receivers when the other of the first and second signals is not available.
 8. The control system for controlling movement of individual hydraulically moveable ends of an elongated tool so as to maintain a selected elevational position between each end of the tool and a reference according to claim 7, in which the sensor is an inclinometer mounted on the tool.
 9. The control system for controlling movement of individual hydraulically moveable ends of an elongated tool so as to maintain a selected elevational position between each end of the tool and a reference according to claim 7, in which the control circuit maintains the tool in an orientation such that the third signal remains substantially constant when one of the first and second signals from the elevation receivers is not available, whereby the slope of the tool along its length from the first end to the second end also is maintained substantially constant.
 10. The control system for controlling movement of individual hydraulically moveable ends of an elongated tool so as to maintain a selected elevational position between each end of the tool and a reference according to claim 7, in which the inclinometer is a pendulum sensor with a low pass filtered output.
 11. A method of controlling the elevational position of hydraulically moveable ends of a tool in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, comprising the steps of: (a) selecting a desired elevational position of the tool with respect to the reference; (b) sensing with the elevation receivers the position of the ends of the tool in relation to the reference; (c) sensing the orientation of the tool along its length from one end to the other; and (d) controlling the elevational positions of the ends of the tool using the sensed positions of the ends of the tool in relation to the reference when such positions are both known, and controlling the elevational positions of the ends of the tool using the sensed position of one of the ends of the tool and the sensed orientation of the tool along its length from one end to the other when such positions are not both known.
 12. The method of controlling the elevational position of hydraulically moveable ends of a tool in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, according to claim 11, further comprising the steps of: (e) detecting lateral movement of the tool generally in the direction of the length of the tool; and (f) discontinuing controlling the elevational positions of the ends of the tool using the sensed orientation of the tool until the lateral movement of the tool generally in the direction of the length of the tool is terminated.
 13. The method of controlling the elevational position of hydraulically moveable ends of a tool in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, according to claim 11, in which the step of sensing the orientation of the tool along its length includes the step of sensing the orientation of the tool using an inclinometer.
 14. The method of controlling the elevational position of hydraulically moveable ends of a tool in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, according to claim 11, in which the elevation receivers are light detectors and in which the reference is a rotating beam of light.
 15. The method of controlling the elevational position of hydraulically moveable ends of a tool in relation to a reference detected by elevation receivers attached to the ends of the tool, when reception of one of the elevation receivers of the reference is interrupted, according to claim 11, in which the elevation receivers are laser light detectors and in which the reference is a rotating beam of laser light. 